[54.03] The Giant X-Ray Flare of NGC 5905: Tidal Disruption of a Star, a Brown Dwarf, or a Planet?

L. -X. Li, R. Narayan (Harvard), K. Menou (Virginia)

We model the 1990 giant X-ray flare of the quiescent galaxy
NGC 5905 as the tidal disruption of a star by a supermassive
black hole. From the observed rapid decline of the
luminosity, over a timescale of a few years, we argue that
the flare was powered by the fallback of debris rather than
subsequent accretion via a thin disk. The fallback model
allows constraints to be set on the black hole mass and the
mass of debris. The latter must be very much less than a
solar mass to explain the very low luminosity of the flare.
The observations can be explained either as the partial
stripping of the outer layers of a low-mass main sequence
star or as the disruption of a brown dwarf or a giant
planet. We find that the X-ray emission in the flare must
have originated within a small patch rather than over the
entire torus of circularized material surrounding the black
hole. We suggest that the patch corresponds to the ``bright
spot'' where the stream of returning debris impacts the
torus. Interestingly, although the peak luminosity of the
flare was highly sub-Eddington, the peak flux from the
bright spot was close to the Eddington limit. We speculate
on the implications of this result for observations of other
flare events.